Multi-site land mobile radio systems typically utilize leased communication lines to interconnect radio repeater infrastructure devices with a central call control server. The recurring costs of the leased communication lines, as well as the capital investment required to deploy multiple radio repeater infrastructure devices and a specialized call control server can result in relatively high system costs. Multi-site land mobile radio systems are primarily utilized to provide emergency communications to police officers, fire fighters and other emergency responders.
Professional and commercial entities, such as retail store chains, school systems, utilities companies, transportation companies and generation companies, can also benefit from the use of multi-site land mobile radio systems but, due to the recurring costs and the required capital investment, such entities generally do not deploy such systems. Companies who operate over large geographic areas or in different regions may require hundreds or even thousands of radio repeater infrastructure devices to implement a suitable multi-site land mobile radio system. Moreover, such a system would require multiple central call servers, which themselves would need to be connected over separate leased lines, thus creating significant additional operational expenses.
One alternative for enabling communications between users of such entities are dispatch systems designed to operate over a wide area network (WAN) that includes multiple physical infrastructure devices distributed over a wide area. At each physical infrastructure device, minimal complexity infrastructure devices (e.g., base stations) are provided that are designed to communicate with one another over a wired network and are designed to communicate with wireless communication devices (WCDs) wirelessly or over-the-air (OTA). An infrastructure device provided at a particular physical site can locate and establish connections to other infrastructure devices deployed at other physical sites directly over the Internet (or other WAN). As such, the infrastructure devices can communicate with each other without communicating through a centralized call control center, such as a Mobile Switching Center (MSC), or public telephone network, etc. This greatly reduces the costs for the entities who purchase the infrastructure devices to set up a dispatch system. Once the infrastructure devices have established a connection with one another other over the Internet, wireless communication devices located at one particular physical site can then communicate (via the infrastructure device) with other wireless communication devices located at the other physical sites. In many cases, such networks also support “group call” and/or push-to-talk functionality for allowing simultaneous communications to a group of users.
Mobile Internet Protocol (MIP)
Mobile IP (MIP) is an Internet Engineering Task Force (IETF) standard communications protocol that is designed to allow mobile devices to move from one network to another while maintaining a permanent IP address. Using Mobile IP, nodes may change their point-of-attachment to the Internet without changing their IP address. In the MIP, a mobile node (MN) can have two addresses—a permanent home address and a care-of-address, which is associated with the network the mobile node is visiting. Each MN is identified by its home address disregarding its current location in the Internet. When a MN is away from its home agent (HA), the MN is associated with a care-of address which gives information about its current location.
Two other entities in the MIP are IP nodes (e.g., routers) referred to as a home agent and a foreign agent. A home agent (HA) stores information about mobile nodes whose permanent address is in the HA's network. The HA serves as the anchor point for communication with the MN, and tunnels packets from Corresponding Nodes (CNs) towards the current care of address of the MN and vice-versa. A foreign agent (FA) stores information about mobile nodes visiting its network. FAs also advertise care-of addresses, which are used by MIP. The FA periodically advertises its presence wirelessly and waits for a solicitation message from a roaming MN.
The MIP specifies how a MN registers with its home agent and how the home agent routes datagrams to the mobile node through a tunnel. For example, when MN roams to a new subnet, it must discover and register itself with a nearby FA. The MN issues a wireless registration request to trigger the registration process. The FA forwards that request to that client's original HA. If the request is accepted, a tunnel is established between the HA and FA to relay incoming packets sent to the client's original IP address. Wired messages can then be exchanged between the HA and the FA.
A node wanting to communicate with the MN uses the home address of the MN to send packets (e.g., data packets, voice or audio packets, video packets). When the HA receives the packets, the HA uses a table to determine their destination and tunnels (forwards or redirects) the packets to the MN's care-of address (i.e., the FA in the MN's new subnet) with a new IP header, preserving the original IP header. The packets are decapsulated at the end of the tunnel to remove the added IP header and delivered to the MN.
By contrast, when acting as sender, MN sends packets to the destination node through the FA. The FA can route outbound packets through the tunnel from the FA to HA, and then on to their destination node. This is known as triangular routing since packets take a “triangle routing path” that involves communications between the MN, its FA and the HA of the destination node. As such, in MIP, packets are always routed to the HA first and never directly to the MN.
Although MIP preserves subnet connectivity for a roaming MN, the MIP always involves communicating through the HA of the MN. Moreover, the MN must first regain over the air connectivity with its new FA before an agent discovery phase begins. Furthermore, the registration process involves wire line and wireless communication. The MIP architecture works well for non-real time data, but encounters problems when used for real time data and voice data due to relatively long latency. These characteristics of the MIP can result in considerable reconnection time, longer roaming delays and increased latency. The amount of packet loss can make the MIP unsuitable for use in wide area networks such as those described above. Moreover, the performance of MIP is poor when used for low-latency group voice calls, where there are multiple destinations that are potentially mobile and can be at any site that is part of the network.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.